I went for isofix because I decided having to do the seatbelt up when dd1 was not in it would be a faff - twice a day at least for me as I have to drive her to pre-school. (you need to do this with non isofix ones as the seatbelt is what holds them in & not strapped in they would become a missile in the car in an emergency stop situation.)

I'm very pleased with it & dd1 is very comfy.

Only slight downside is that although it is held firmly in the car the top sort of flops forwards, I have got round this by securing the top with the car headrest - a strap or piece of string around it will have to do the same job as she gets taller & the seat gets bigger.

I suspect that this would be a problem with all of these types of car seats though. & as I said I really am pleased with it.